Device-to-device (D2D) technology is attractive and getting a lot of attention because of its ability to offer new services, improve system throughput, and offer a better user experience. Potential use cases for D2D have been identified by 3GPP SA WG1 in [1]. Standardization work is ongoing in 3GPP.
There are two main identified D2D technologies: discovery and communication. In discovery, a user equipment (UE) attempts to discover neighboring UEs in its vicinity, either on its own or directed by the base station or enhanced Node B (eNB). In communication, one UE directly communicates with another UE without the data transiting through the eNB.